For towing trailers, by vehicles, use is generally made of ball type couplings having a tow ball mounted to the vehicle and cooperating tow coupling attached to the trailer. The coupling couples to the ball in a manner enabling a substantial degree of rotational movement of the coupling and trailer relative to the vehicle and about the upright vertical axis of the ball. This assists in manoeuvring the vehicle and trailer around corners. A substantial degree of such rotational movement about a horizontal axis is also permitted, of assistance for example in traverse of the vehicle and trailer over road humps and dips.
In some applications however, it may be undesirable to permit free relatively free rotational movement between the ball and coupling. The following publications, for example, describe devices for collecting debris from a ground surface:
International Patent Application No. PCT/AU2005/000692;
International Patent Application No. PCT/AU1995/00629;
International Patent Application No. PCT/AU1998/00001;
International Patent Application No. PCT/AU2008/001252;
International Patent Application No. PCT/AU2009/000149.
The disclosures of these are herby incorporated to form part of the disclosure of this application.
These devices are in the form of a generally planar structure which is towed over the ground surface such that debris on the ground surface moves upwardly through apertures in the structure to be deposited on an upper collection surface of it. While it is possible to use any conventional method of coupling these structures to vehicles, for towing, such as to use ball couplings as mentioned, it has been found that efficiency of collection may be improved by at least biasing e.g. the leading edge of the structure to a relatively fixed location with respect to the ground surface rather than permitting relatively free movement as occurs with ball-type couplings as described.